JOHANNESBURG, South Africa (CNN) -- A summit of regional leaders in South Africa ended Sunday with no agreement to end Zimbabwe's political crisis.

Robert Mugabe (left) and Morgan Tsvangirai met last month for the first round of talks.

But the leaders said they believe there is a basis for a power-sharing deal, and called on both sides to sign it.

South African President Thabo Mbeki, the lead Zimbabwe negotiator for the 14-member Southern African Development Community (SADC), said the group wants Zimbabwe's government leaders and opposition to "conclude the negotiations ... as a matter of urgency."

"It's clearly not possible to say when negotiations will be concluded," he told reporters after the summit. "It's a matter of negotiating parties reconvening."